The present embodiments relate to physically-based volume rendering. Data representing a volume is rendered for visualization. In a medical imaging example, an image from a three-dimensional (3D) scan of a patient is rendered.
Physically-based visualization techniques produce global illumination effects in computer-generated graphics that mimic the real-world interaction of light with various 3D objects or tissues. Monte Carlo path tracing is a useful rendering technique for light transport computations, where the natural light phenomena are modeled using a stochastic process. The physically-based volume rendering results in physically plausible images that are often easier for the human brain to interpret when compared to the more analytical images from traditional volume rendering, such as ray casting or direct volume rendering. For example, subtle ambient light occlusions, soft shadows, color bleeding, and depth of field resulting from physically-based volume rendering provide important depth cues for the spatial understanding of 3D relationships between structures in a single 2D image, whereas simpler visualization techniques may require additional interaction with the viewing parameters (e.g., moving the virtual camera around the 3D data) to obtain the same spatial information from the image parallax.
Evaluation of the rendering integral in physically-based volume rendering may require thousands of stochastic samples per pixel to produce an acceptably noise-free image. Depending on the rendering parameters and implementing processor, producing one photorealistic image with physically-based volume rendering may be on the order of seconds for interactive workflows and multiple hours for production-quality images. Devices with less processing power, such as mobile devices, may take even longer. These rendering times may result in overly long interaction times as the user attempts to refine the rendering to achieve the desired results.